This invention relates to a method and apparatus for processing images having color combinations. Such combinations may be embodied in, for example, a black object being printed within a color object or in a black object that includes drops of process color within the object. In these circumstances, undesired image artifacts and halos are eliminated in images that include black portions that are adjacent color portions, and/or improved printed edges are created, by offsetting the corresponding black pixels relative to the color pixels and etching preselected pixels from the image before printing.
While the invention is particularly directed to the art of image rendering, and will be thus described with specific reference thereto, it will be appreciated that the invention may have usefulness in other fields and applications. For example, the invention may be used in any image processing application where difficulties arise in the image at the border of different types or colors of pixels.
By way of background, a variety of difficulties arise when printing a color image, particularly where it is desired to print black objects among or within color portions of the image. As such, to print improved black colors, it has become desirable to print a black drop on top of a color drop. However, slight differences in alignment can have large effects on the amount of color that shows through. Moreover, printing drop on drop results in a color density on the printed page that could be improved. That is, portions of the page (i.e. between drops) can remain uncovered.
Therefore, when printing single large or multiple small ink drops to render a color image, it is advantageous to offset black drops from color drops by, for example, one-half pixel. This helps maintain color stability. That is, a better black color can be realized on the print medium.
A problem with offsetting alone, however, is that it may create undesired image characteristics and artifacts. In this regard, the printed image may include edges that are less than crisp or edges that are inconsistent from one side of the printed object to the other. Moreover, the image may experience inter-color bleed or asymmetric halos when printing color portions of the image adjacent black portions of the image.
The present invention contemplates a new and improved method and apparatus that resolve the above-referenced difficulties and others.